使用urllib2时是否可以轻松限制kbps？
如果是这样，您可以直接向我推荐的任何代码示例或资源将不胜感激。
最佳答案
urlretrieve(url, filename=None, reporthook=None, data=None)模块中有urllib函数。
如果将reporthook -function/object实现为token bucket或泄漏的存储桶，则将具有全局速率限制。
编辑:通过仔细检查，我发现用reporthook进行全局速率限制并不像我想的那么容易。仅给reporthook提供下载量和总大小，仅靠它们本身不足以提供与 token 桶一起使用的信息。解决该问题的一种方法是，将最新下载的数量存储在每个速率限制器中，但使用全局 token 桶。
编辑2:将两个代码合并为一个示例。
"""Rate limiters with shared token bucket."""
import os
import sys
import threading
import time
import urllib
import urlparse
class TokenBucket(object):
"""An implementation of the token bucket algorithm.
source: http://code.activestate.com/recipes/511490/
>>> bucket = TokenBucket(80, 0.5)
>>> print bucket.consume(10)
True
>>> print bucket.consume(90)
False
"""
def __init__(self, tokens, fill_rate):
"""tokens is the total tokens in the bucket. fill_rate is the
rate in tokens/second that the bucket will be refilled."""
self.capacity = float(tokens)
self._tokens = float(tokens)
self.fill_rate = float(fill_rate)
self.timestamp = time.time()
self.lock = threading.RLock()
def consume(self, tokens):
"""Consume tokens from the bucket. Returns 0 if there were
sufficient tokens, otherwise the expected time until enough
tokens become available."""
self.lock.acquire()
tokens = max(tokens,self.tokens)
expected_time = (tokens - self.tokens) / self.fill_rate
if expected_time <= 0:
self._tokens -= tokens
self.lock.release()
return max(0,expected_time)
@property
def tokens(self):
self.lock.acquire()
if self._tokens < self.capacity:
now = time.time()
delta = self.fill_rate * (now - self.timestamp)
self._tokens = min(self.capacity, self._tokens + delta)
self.timestamp = now
value = self._tokens
self.lock.release()
return value
class RateLimit(object):
"""Rate limit a url fetch.
source: http://mail.python.org/pipermail/python-list/2008-January/472859.html
(but mostly rewritten)
"""
def __init__(self, bucket, filename):
self.bucket = bucket
self.last_update = 0
self.last_downloaded_kb = 0
self.filename = filename
self.avg_rate = None
def __call__(self, block_count, block_size, total_size):
total_kb = total_size / 1024.
downloaded_kb = (block_count * block_size) / 1024.
just_downloaded = downloaded_kb - self.last_downloaded_kb
self.last_downloaded_kb = downloaded_kb
predicted_size = block_size/1024.
wait_time = self.bucket.consume(predicted_size)
while wait_time > 0:
time.sleep(wait_time)
wait_time = self.bucket.consume(predicted_size)
now = time.time()
delta = now - self.last_update
if self.last_update != 0:
if delta > 0:
rate = just_downloaded / delta
if self.avg_rate is not None:
rate = 0.9 * self.avg_rate + 0.1 * rate
self.avg_rate = rate
else:
rate = self.avg_rate or 0.
print "%20s: %4.1f%%, %5.1f KiB/s, %.1f/%.1f KiB" % (
self.filename, 100. * downloaded_kb / total_kb,
rate, downloaded_kb, total_kb,
)
self.last_update = now
def main():
"""Fetch the contents of urls"""
if len(sys.argv) < 4:
print 'Syntax: %s rate url1 url2 ...' % sys.argv[0]
raise SystemExit(1)
rate_limit = float(sys.argv[1])
urls = sys.argv[2:]
bucket = TokenBucket(10*rate_limit, rate_limit)
print "rate limit = %.1f" % (rate_limit,)
threads = []
for url in urls:
path = urlparse.urlparse(url,'http')[2]
filename = os.path.basename(path)
print 'Downloading "%s" to "%s"...' % (url,filename)
rate_limiter = RateLimit(bucket, filename)
t = threading.Thread(
target=urllib.urlretrieve,
args=(url, filename, rate_limiter))
t.start()
threads.append(t)
for t in threads:
t.join()
print 'All downloads finished'
if __name__ == "__main__":
main()
关于python - 用urllib2节流，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/456649/